FIG. 13 shows a steering mechanism of a common automobile. The parts designated by a and b in this drawing are telescopic shafts. The telescopic shaft a is formed by spline fitting a male shaft and a female shaft. The telescopic shaft a of this type is required to have the properties of absorbing axial displacement that occurs while the automobile is running and preventing transmission of the displacement and vibration to the steering wheel. Such properties are generally required in the case that the vehicle body has a sub-frame structure and the portion c on which the upper portion of the steering mechanism is secured and the frame e on which the steering rack d is secured are constructed as separate members that are steadily joined by an elastic member f such as a rubber. In some other cases, the telescopic function is required in order for an assembling engineer in charge of joining a steering shaft joint g to a pinion shaft h, to fit and secure the telescopic shaft to the pinion shaft after retracting it. The telescopic shaft b provided in the upper portion of the steering mechanism also has a male shaft and female shaft spline connected. The telescopic shaft b is required to be extended and retracted in the axial direction in order for the driver to change and adjust the position of the steering wheel i in the axial direction to achieve the optimum position for driving the automobile. In all the above-mentioned cases, it is demanded to reduce the rattling noise of the spline portion of the telescopic shaft, to soften rattly feeling of the steering wheel and to decrease sliding resistance of the telescopic shaft when it is slid in the axial direction.
In view of the above, EP1078843A1 teaches to fit multiple sets of torque transmission members (column-like members) in multiple sets of axial grooves formed on the outer circumferential surface of the male shaft and the inner circumferential surface of the female shaft.
Each set of the torque transmission members (cylindrical members) include a plurality of needle rollers arranged along the axial direction.
Thus, play between the male shaft and the female shaft can be eliminated when the torque is not transmitted, and the male shaft and the female shaft can be slid in the axial direction with a stable slide load without play. In addition, when the torque is transmitted, the male shaft and the female shaft can transmit the torque with high rigidity while eliminating play in the rotational direction.
Furthermore, between the plurality of needle rollers arranged along the axial direction, there is provided adjusting members made of a resin, which is adapted to absorb the clearance (or play) between the needle rollers.
However, although EP1078843A1 teaches to absorb the clearance between the plurality of needle rollers by means of adjusting members provided between the needle rollers arranged along the axial direction, clearance sometimes remains between the needle rollers, which may cause a knocking sound.